class Stack(object):
    def __init__(self,limit=10):
        self.stack=[]
        self.limit=limit
    def is_empty(self):
        return len(self.stack) == 0
    def push(self,data):
        if len(self.stack) >= self.limit:
            print('栈溢出')
        else:
            self.stack.append(data)
    def pop(self):
        if self.stack:
            return self.stack.pop()
        else:
            print('空栈不能被弹出')
    def top(self):
        if self.stack:
            return self.stack[-1]
    def size(self):
        return len(self.stack)
stack=Stack()
print(stack.size())

stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
print(stack.size())
print(stack.is_empty())
print(stack.top())
print(stack.pop())
print(stack.top())
